/* Copyright (C) 2002, 2003, 2006, 2007, 2009 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. */ #include <errno.h> #include <fcntl.h> #include <mntent.h> #include <paths.h> #include <pthread.h> #include <search.h> #include <semaphore.h> #include <stdarg.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mman.h> #include <sys/stat.h> #include <sys/statfs.h> #include <linux_fsinfo.h> #include "semaphoreP.h" #include "../../libc/misc/internals/tempname.h" /* Compatibility defines. */ #define __endmntent endmntent #define __fxstat64(vers, fd, buf) fstat64(fd, buf) #define __getmntent_r getmntent_r #define __setmntent setmntent #define __statfs statfs #define __libc_close close #define __libc_open open #define __libc_write write /* Information about the mount point. */ struct mountpoint_info mountpoint attribute_hidden; /* This is the default mount point. */ static const char defaultmount[] = "/dev/shm"; /* This is the default directory. */ static const char defaultdir[] = "/dev/shm/sem."; /* Protect the `mountpoint' variable above. */ pthread_once_t __namedsem_once attribute_hidden = PTHREAD_ONCE_INIT; /* Determine where the shmfs is mounted (if at all). */ void attribute_hidden __where_is_shmfs (void) { char buf[512]; struct statfs f; struct mntent resmem; struct mntent *mp; FILE *fp; /* The canonical place is /dev/shm. This is at least what the documentation tells everybody to do. */ if (__statfs (defaultmount, &f) == 0 && f.f_type == SHMFS_SUPER_MAGIC) { /* It is in the normal place. */ mountpoint.dir = (char *) defaultdir; mountpoint.dirlen = sizeof (defaultdir) - 1; return; } /* OK, do it the hard way. Look through the /proc/mounts file and if this does not exist through /etc/fstab to find the mount point. */ fp = __setmntent ("/proc/mounts", "r"); if (__builtin_expect (fp == NULL, 0)) { fp = __setmntent (_PATH_MNTTAB, "r"); if (__builtin_expect (fp == NULL, 0)) /* There is nothing we can do. Blind guesses are not helpful. */ return; } /* Now read the entries. */ while ((mp = __getmntent_r (fp, &resmem, buf, sizeof buf)) != NULL) /* The original name is "shm" but this got changed in early Linux 2.4.x to "tmpfs". */ if (strcmp (mp->mnt_type, "tmpfs") == 0 || strcmp (mp->mnt_type, "shm") == 0) { /* Found it. There might be more than one place where the filesystem is mounted but one is enough for us. */ size_t namelen; /* First make sure this really is the correct entry. At least some versions of the kernel give wrong information because of the implicit mount of the shmfs for SysV IPC. */ if (__statfs (mp->mnt_dir, &f) != 0 || f.f_type != SHMFS_SUPER_MAGIC) continue; namelen = strlen (mp->mnt_dir); if (namelen == 0) /* Hum, maybe some crippled entry. Keep on searching. */ continue; mountpoint.dir = (char *) malloc (namelen + 4 + 2); if (mountpoint.dir != NULL) { char *cp = mempcpy (mountpoint.dir, mp->mnt_dir, namelen); if (cp[-1] != '/') *cp++ = '/'; cp = stpcpy (cp, "sem."); mountpoint.dirlen = cp - mountpoint.dir; } break; } /* Close the stream. */ __endmntent (fp); } /* Comparison function for search of existing mapping. */ int attribute_hidden __sem_search (const void *a, const void *b) { const struct inuse_sem *as = (const struct inuse_sem *) a; const struct inuse_sem *bs = (const struct inuse_sem *) b; if (as->ino != bs->ino) /* Cannot return the difference the type is larger than int. */ return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1); if (as->dev != bs->dev) /* Cannot return the difference the type is larger than int. */ return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1); return strcmp (as->name, bs->name); } /* The search tree for existing mappings. */ void *__sem_mappings attribute_hidden; /* Lock to protect the search tree. */ int __sem_mappings_lock attribute_hidden = LLL_LOCK_INITIALIZER; /* Search for existing mapping and if possible add the one provided. */ static sem_t * check_add_mapping (const char *name, size_t namelen, int fd, sem_t *existing) { sem_t *result = SEM_FAILED; /* Get the information about the file. */ #ifdef __UCLIBC_HAS_LFS__ struct stat64 st; if (__fxstat64 (_STAT_VER, fd, &st) == 0) #else struct stat st; if (fstat (fd, &st) == 0) #endif { /* Get the lock. */ lll_lock (__sem_mappings_lock, LLL_PRIVATE); /* Search for an existing mapping given the information we have. */ struct inuse_sem *fake; fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen); memcpy (fake->name, name, namelen); fake->dev = st.st_dev; fake->ino = st.st_ino; struct inuse_sem **foundp = tfind (fake, &__sem_mappings, __sem_search); if (foundp != NULL) { /* There is already a mapping. Use it. */ result = (*foundp)->sem; ++(*foundp)->refcnt; } else { /* We haven't found a mapping. Install ione. */ struct inuse_sem *newp; newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen); if (newp != NULL) { /* If the caller hasn't provided any map it now. */ if (existing == SEM_FAILED) existing = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); newp->dev = st.st_dev; newp->ino = st.st_ino; newp->refcnt = 1; newp->sem = existing; memcpy (newp->name, name, namelen); /* Insert the new value. */ if (existing != MAP_FAILED && tsearch (newp, &__sem_mappings, __sem_search) != NULL) /* Successful. */ result = existing; else /* Something went wrong while inserting the new value. We fail completely. */ free (newp); } } /* Release the lock. */ lll_unlock (__sem_mappings_lock, LLL_PRIVATE); } if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED) { /* Do not disturb errno. */ INTERNAL_SYSCALL_DECL (err); INTERNAL_SYSCALL (munmap, err, 2, existing, sizeof (sem_t)); } return result; } sem_t * sem_open (const char *name, int oflag, ...) { char *finalname; sem_t *result = SEM_FAILED; int fd; /* Determine where the shmfs is mounted. */ __pthread_once (&__namedsem_once, __where_is_shmfs); /* If we don't know the mount points there is nothing we can do. Ever. */ if (mountpoint.dir == NULL) { __set_errno (ENOSYS); return SEM_FAILED; } /* Construct the filename. */ while (name[0] == '/') ++name; if (name[0] == '\0') { /* The name "/" is not supported. */ __set_errno (EINVAL); return SEM_FAILED; } size_t namelen = strlen (name) + 1; /* Create the name of the final file. */ finalname = (char *) alloca (mountpoint.dirlen + namelen); mempcpy (mempcpy (finalname, mountpoint.dir, mountpoint.dirlen), name, namelen); /* If the semaphore object has to exist simply open it. */ if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0) { try_again: fd = __libc_open (finalname, (oflag & ~(O_CREAT|O_ACCMODE)) | O_NOFOLLOW | O_RDWR); if (fd == -1) { /* If we are supposed to create the file try this next. */ if ((oflag & O_CREAT) != 0 && errno == ENOENT) goto try_create; /* Return. errno is already set. */ } else /* Check whether we already have this semaphore mapped and create one if necessary. */ result = check_add_mapping (name, namelen, fd, SEM_FAILED); } else { /* We have to open a temporary file first since it must have the correct form before we can start using it. */ char *tmpfname; mode_t mode; unsigned int value; va_list ap; try_create: va_start (ap, oflag); mode = va_arg (ap, mode_t); value = va_arg (ap, unsigned int); va_end (ap); if (value > SEM_VALUE_MAX) { __set_errno (EINVAL); return SEM_FAILED; } /* Create the initial file content. */ union { sem_t initsem; struct new_sem newsem; } sem; sem.newsem.value = value; sem.newsem.private = 0; sem.newsem.nwaiters = 0; /* Initialize the remaining bytes as well. */ memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0', sizeof (sem_t) - sizeof (struct new_sem)); tmpfname = (char *) alloca (mountpoint.dirlen + 6 + 1); mempcpy (mempcpy (tmpfname, mountpoint.dir, mountpoint.dirlen), "XXXXXX", 7); fd = __gen_tempname (tmpfname, __GT_FILE, mode); if (fd == -1) return SEM_FAILED; if (TEMP_FAILURE_RETRY (__libc_write (fd, &sem.initsem, sizeof (sem_t))) == sizeof (sem_t) /* Map the sem_t structure from the file. */ && (result = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) != MAP_FAILED) { /* Create the file. Don't overwrite an existing file. */ if (link (tmpfname, finalname) != 0) { /* Undo the mapping. */ (void) munmap (result, sizeof (sem_t)); /* Reinitialize 'result'. */ result = SEM_FAILED; /* This failed. If O_EXCL is not set and the problem was that the file exists, try again. */ if ((oflag & O_EXCL) == 0 && errno == EEXIST) { /* Remove the file. */ (void) unlink (tmpfname); /* Close the file. */ (void) __libc_close (fd); goto try_again; } } else /* Insert the mapping into the search tree. This also determines whether another thread sneaked by and already added such a mapping despite the fact that we created it. */ result = check_add_mapping (name, namelen, fd, result); } /* Now remove the temporary name. This should never fail. If it fails we leak a file name. Better fix the kernel. */ (void) unlink (tmpfname); } /* Map the mmap error to the error we need. */ if (MAP_FAILED != (void *) SEM_FAILED && result == MAP_FAILED) result = SEM_FAILED; /* We don't need the file descriptor anymore. */ if (fd != -1) { /* Do not disturb errno. */ INTERNAL_SYSCALL_DECL (err); INTERNAL_SYSCALL (close, err, 1, fd); } return result; }